The present invention relates to center high mounted stoplights (CHMSL) for vehicles.
Since 1985 every U.S. automobile has been required to include a CHMSL as a safety feature. Typically the CHMSL is mounted behind the rear window, either in the roof or on top of the rear deck. In either case, the unfortunate result is partial obstruction of the driver's view through the rear window. U.S. Pat. No. 4,892,369 describes a holographic CHMSL which addresses this problem, and includes a transparent hologram on or near the rear window and a remotely located lamp which delivers light to the hologram. Two specific types of holographic CHMSLs are the floodlit CHMSL described in U.S. Pat. No. 4,916,593, and the trapped beam CHMSL described in pending application Ser. No. 87503, both assigned to the assignee of this application. In the floodlit CHMSL the remotely located lamp projects a beam of light through air to a hologram mounted on the rear window. In the trapped beam CHMSL, lamp light from an incandescent halogen bulb is injected into a thin light guide which carries the light and delivers it to a hologram. This design allows for greater headroom for the rear occupant as well as improved rearward visibility for the driver.
While holographic CHMSLs employing halogen bulbs as the light source are advantageous over a conventional CHMSL in terms of reduced size and greater driver rearward visibility, such CHMSLS require considerable electrical power, their size and weight are not as small as that which is ultimately desired, they dissipate more heat from the bulbs than desired, and the complexity of these devices results in additional cost and manufacturing difficulties.
It would therefore be advantageous to provide a holographic CHMSL which possesses the advantages of the trapped beam CHMSL but which overcomes the aforementioned shortcomings.